Electronically controlled direct fuel injection devices such as electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an electronic fuel injection signal received from an electronic fuel injection control device (controller) or system. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders.
Emission regulations pertaining to engine exhaust emissions are becoming more restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Tailoring the electronic fuel injection current signal waveform and the resulting number of injections and the injection rate of fuel to a combustion chamber during a combustion cycle of the cylinder, as well as the quantity and timing of such fuel injections, is one way to improve emissions and meet higher emissions standards. As a result, multiple fuel injection techniques, wherein the electronic fuel injection signal waveform comprises a plurality of distinct fuel injection signals, have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multiple fuel injections typically involve splitting the total fuel delivery to the cylinder during a particular injection event into separate fuel injections, such as a pilot injection, a main injection, and an anchor injection, where three injections of fuel (a three shot injection) are desired. Each of these injections may also be referred to generally as a shot, and the term shot as used in the art may also refer to the actual fuel injection or to the command current signal (electronic fuel injection current signal), also referred to simply as a fuel injection signal, to a fuel injector indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine performance and emissions control.
During normal operation of an engine, the injection strategies may change several times. Typically each injection strategy will differ slightly from the other injection strategies in both the level of noise and amount of torque produced. In some instances, the transition from one strategy to another may cause a noticeable “step-change” in either or both of these characteristics and/or other characteristics. This sudden change in characteristics is often undesirable.